Microorganisms of the genus Bifidobacterium, alias bifidobacteria, are constituents of the intestinal flora in mammals inclusive of man and it is known that these bacteria per se are not pathogenic but rather antagonizing pathogenic intestinal bacteria in respect of, for example, lactic acid production and nutrient requirement, thus interfering with proliferation of the pathogenic bacteria in the intestinal canal. It is also known that a breast-fed infant in whom these bacteria are present in the form of pure cultures is less susceptible to enteral infection than a bottle-fed infant in whom they are only sparsely present. Based on the above and other findings, many progresses have been made in the research concerning bifidobacteria of late and as more light is cast on the immuno-potentiating effect, prophylactic effect on microbial substitution, and inhibitory effect on carcinogenic substances of these bacteria, their clinical application has been attempted.
Since bifidobacteria must be encouraged to multiply in the intestine in order that their variegated actions may be exploited, much research into substances that could promote growth of bifidobacteria (hereinafter referred to as bifidus factors) is going on with great enthusiasm.
The generally acknowledged requisites of any bifidus factor are that it is not digested and absorbed in the upper digestive tract but reaches the ileum and large intestine and that it is efficiently assimilated by bifidobacteria and hardly utilized by other bacteria. Several substances in the name of bifidus factors have heretofore been proposed and, above all else, incorporation of oligosaccharides in various kinds of foodstuffs is broadly practiced.
However, from the standpoint of said requisites, the oligosaccharides so far reported are not impeccable bifidus factors. Fructooligosaccharides, for instance, have the disadvantage that they are decomposed by gastric acid and partly absorbed from the upper digestive tract. Isomaltooligosaccharides, too, are hydrolyzed by small intestine mucosal enzymes and absorbed there, thus making it mandatory to ingest them in massive doses. Galactooligosaccharides are relatively resistant to acid and heat and not easily digested and absorbed in the upper digestive tract but have the drawback, process-wise, that their yields are low and the costs of production are high. Furthermore, since all of them are sugars, they act as sweeteners when applied to food so that the disadvantage of sweetness alone being emphasized in the food is unavoidable. In addition, the utilization selectivity of bacteria for these saccharides is low. That is to say they are utilized not only by bifidobacteria but also by other intestinal bacteria, thus presenting the problem that a massive intake is necessary for achieving sufficient efficacy.
Having been developed with a view to overcoming the above-mentioned disadvantages of the prior art, this invention has for its object to provide a bifidus factor which is not digested and absorbed in the upper digestive tract, promotes growth of bifidobacteria remarkably, and does so with high selectivity.